diff --git a/llvm/include/llvm/ADT/APFloat.h b/llvm/include/llvm/ADT/APFloat.h
--- a/llvm/include/llvm/ADT/APFloat.h
+++ b/llvm/include/llvm/ADT/APFloat.h
@@ -1036,6 +1036,13 @@
     APFLOAT_DISPATCH_ON_SEMANTICS(next(nextDown));
   }
 
+  /// Negate an APFloat.
+  APFloat operator-() const {
+    APFloat Result(*this);
+    Result.changeSign();
+    return Result;
+  }
+
   /// Add two APFloats, rounding ties to the nearest even.
   /// No error checking.
   APFloat operator+(const APFloat &RHS) const {
diff --git a/llvm/unittests/ADT/APFloatTest.cpp b/llvm/unittests/ADT/APFloatTest.cpp
--- a/llvm/unittests/ADT/APFloatTest.cpp
+++ b/llvm/unittests/ADT/APFloatTest.cpp
@@ -2990,6 +2990,17 @@
   EXPECT_TRUE(Inf.bitwiseIsEqual(neg(NegInf)));
   EXPECT_TRUE(NegQNaN.bitwiseIsEqual(neg(QNaN)));
   EXPECT_TRUE(QNaN.bitwiseIsEqual(neg(NegQNaN)));
+
+  EXPECT_TRUE(NegOne.bitwiseIsEqual(-One));
+  EXPECT_TRUE(One.bitwiseIsEqual(-NegOne));
+  EXPECT_TRUE(NegZero.bitwiseIsEqual(-Zero));
+  EXPECT_TRUE(Zero.bitwiseIsEqual(-NegZero));
+  EXPECT_TRUE(NegInf.bitwiseIsEqual(-Inf));
+  EXPECT_TRUE(Inf.bitwiseIsEqual(-NegInf));
+  EXPECT_TRUE(NegInf.bitwiseIsEqual(-Inf));
+  EXPECT_TRUE(Inf.bitwiseIsEqual(-NegInf));
+  EXPECT_TRUE(NegQNaN.bitwiseIsEqual(-QNaN));
+  EXPECT_TRUE(QNaN.bitwiseIsEqual(-NegQNaN));
 }
 
 TEST(APFloatTest, ilogb) {